1. Field of the Invention
The present invention relates to a method for effectively forming a contact hole and a capacitor in a semiconductor integrated circuit.
2. Description of the Related Art
In a semiconductor integrated circuit, a multilayer wiring structure is used, it is necessary to form a contact hole for connecting with wirings one another and an element such as a capacitor (condenser). To obtain the multilayer wiring structure, an interlayer insulator is formed in general, so that insulation and capacitance between the wirings are decreased. In a portion required to connect with the wirings one another, a contact hole is formed in the interlayer insulator. When a capacitor is formed, the interlayer insulator itself may be used as dielectric. However, since the interlayer insulator is used to decrease insulation and capacitance between the wirings, when the interlayer insulator is used as dielectric of the capacitor, an area of the capacitor is extremely large and thus loss is great in a circuit design.
If an interlayer insulator is thin, the capacitor having a large capacitance can be formed in the same area. However, to achieve this, it is necessary to remove the interlayer insulator completely in a contact hole forming portion and to etch the interlayer insulator suitably (until a suitable thickness required to form a capacitor) in a capacitor forming portion. Thus, it is impossible to use such the capacitor actually in mass production process.
To operate a capacitor effectively, it is required that a thickness of a portion of an interlayer insulator used as dielectric is ⅕ to 1/50 thinner than an initial thickness of an interlayer insulator. If a capacitance of a capacitor is 100 times larger than that of an intersection portion of a normal wiring and an interlayer insulator formed in a portion of the capacitor has the same thickness as the intersection portion of the normal wiring, it is required that an area of the capacitor is 1000 times larger than that of the intersection portion of the wiring. On the other hand, if a thickness of the portion of the capacitor is 1/10, the area of the capacitor is 100 times larger than that of the intersection portion, and thus it is effective in integration of elements. However, for example, it is impossible to etch an interlayer insulator by 90% in thickness to and remain it by only 10% in thickness. Thus, precision control cannot be performed substantially in a desired area.